Metals, electromigration

Park H, Li AKL, Alivisatos AP, Park J, McEuen PL (1999) Fabrication of metallic electrodes with nanometer separation by electromigration. Appl Phys Lett 75 301... 

The circular microhotplate presented in Sect. 4.1 features an upper sensor operating temperature limit of 350 °C, which is imposed by the CMOS metallization. At higher temperatures, electromigration, especially in the heater structures, will occur. 

Electrokinetic soil treatment is a commercially available in situ technology for the removal of metals and organic compounds. The application of direct current (DC) in a porous medium leads to two transport mechanisms electromigration and electro-osmosis. The combination of these two transport phenomena results in the movement of contaminant ions toward either the cathode or anode. Nonionic contaminants are transported by electro-osmosis alone. 

ISOTRON Corporation s electrokinetic decontamination process is a patented, in situ process for the removal of contaminants from soil, groundwater, and porous concrete. The technology applies a low-intensity direct current (DC) across electrode pairs to facilitate electromigration and electro-osmosis of contaminants. The process works primarily on highly soluble ionized inorganics including alkah metals, chlorides, nitrates, and phosphates. Heavy metals such as lead, mercury, cadmium, and chromium have also responded favorably. 

Electrophoresis is one of many electromigrational separation techniques which include isotachophoresis, immunoelectrophoresis and isoelectric focussing that have been used to separate various species on the basis of their different mobility in an electric field. These techniques can be used not only to achieve separations but also it is possible to identify the ligand bound to the metal. This can be done by comparing the isoelectric points, immunological behaviours, extent of mobilities or step heights of the sample constituents with those of well-characterised standards. A difficulty, however, is in the determination of the metal constituent itself. Except in the case of radioisotopes, the activities of which can be easily measured, non-radioactive elements can be detected only after further separation steps. 

An applied electrical potential gradient can induce diffusion (electromigration) in metals due to a cross effect between the diffusing species and the flux of conduction electrons that will be present. When an electric field is applied to a dilute solution of interstitial atoms in a metal, there are two fluxes in the system a flux of conduction electrons, Jq, and a flux of the interstitials, J. For a system maintained at constant temperature with Fq = -V = E, Eq. 2.21 gives... 

The vacancy current is therefore due solely to the cross term arising from the current of conduction electrons (which is proportional to E). The coupling coefficient for the vacancies is the off-diagonal coefficient Lvq which can be evaluated using the same procedure as that which led to Eq. 3.54 for the electromigration of interstitial atoms in a metal. Therefore, if (5V) is the average drift velocity of the vacancies induced by the current and Mv is the vacancy mobility,... 

Common concerns involving metal contacts include adhesion to the substrate, degradation due to corrosion, electromigration etc. and the tendency for some multilayered metallization schemes to undergo rapid interdiffusion. Surface analysis has been used to address a number of these problems. 

Runnells, D. D., and Wahli, C. (1993) In Situ Electromigration as a Method for Removing Sulfate, Metals, and Other Contaminants from Groundwater, Ground Water Monitoring Remediation, 13(1), 121-129. 

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